This month, US President Joe Biden, joined by French President Emmanuel Macron, stood on the Normandy bluffs to commemorate the young men who clambered ashore 80 years ago into a hail of Nazi gunfire because “they knew beyond any doubt there are things worth fighting and dying for.” Among those things, Biden said, were freedom, democracy, America and the world, “then, now and always.” It was a moving moment as Macron spoke of the “bond of blood” between France and America, but just a few weeks later, the ability of either leader to hold the line in defense of their...